1. Field of the Invention
The present invention relates to a device using a piezoelectric/electrostrictive film, and more particularly relates to the structure of a piezoelectric/electrostrictive device for improving an operational characteristic of a piezoelectric/electrostrictive device in an element for converting electrical energy into mechanical energy such as mechanical displacement, mechanical force, and vibration, and for converting in reverse. Concretely, the present invention relates to a piezoelectric/electrostrictive device to be preferably utilized in a variety of sensors, such as transducers, a variety of actuators, frequency-region functional components (filters), transformers, vibrators and resonators for communication and motive power, oscillators, discriminators, ultrasonic sensors and acceleration sensors, angular velocity sensors and impact sensors, mass sensors, or the like, and moreover to be applied to unimorph- and bimorph-type elements used for servo displacement elements described in xe2x80x9cFrom Foundation up to Application of Piezoelectric/Electrostrictive Actuatorxe2x80x9d written by Kenji Uchino (edited by Japan Industrial Technique Center and published by MORIKAWA SHUPPAN), and to be preferably employed to a variety of actuators used for mechanisms for displacement and positioning adjustment and angle adjustment of a variety of precision components, or the like, of an optical apparatus and a precision apparatus, or the like.
2. Description of the Related Art
Recently, there has been a requirement for a displacement control element for adjusting an optical-path length or a position in sub-micron order in optical and magnetic recording fields and precision machining fields. Responding to the requirement, development has been progressed of a piezoelectric/electrostrictive actuator or the like which is an element utilizing a displacement based on the reverse piezoelectric effect or the electrostrictive effect caused when an electric field is applied to a piezoelectric/electrostrictive material such as a ferroelectric substance or the like.
In a magnetic recording field represented by a hard disk, among the above mentioned fields, particularly a storage capacity has been remarkably increased in these years, and this is because an attempt has been made to increase the recording density per se by increasing the number of recording tracks for more effective use of recording mediums, in addition to the improvement of a recording method of write/read.
So far, such attempt has been made mainly on the improvement of a voice coil motor, however, an attempt is introduced as a new technique, for example, in a preprint manuscript of xe2x80x9c1997 International Conference on Solid-State Sensors and Actuatorsxe2x80x9d of xe2x80x9cTRANSDUCERS ""97xe2x80x9d, pp. 1081-1084, that an electrostatic-type micro-actuator fabricated by micro-machine processing of Si or Ni is applied to the tracking system of a hard-disk magnetic head.
Moreover, Japanese Unexamined Patent Publication No. 10-136665 discloses a piezoelectric/electrostrictive actuator 101, as shown in FIG. 26, wherein a fixing portion 103 and a movable portion 104 and at least one beam portion 102 constituted therewith are integrally formed by arranging at least one hole on a plate-shaped body composed of a piezoelectric/electrostrictive material, a displacement generating portion is constituted by providing an electrode layer 105 such that an expansion and a contraction is caused in a direction connecting the fixing portion 103 with the movable portion 104 on at least a part of the at least one beam portion 102, and a displacement of the movable portion 104 relative to the fixing portion 103 generated by the expansion or the contraction of the displacement generating portion becomes an arc-shaped displacement or a rotational displacement in-plane of the plate-shaped body.
However, with a conventional art for positioning a recording head primarily using a voice coil motor, it is difficult to accurately position the recording head so as to accurately trace tracks thereof by increasing the number of the tracks, in order to respond to the further increase in capacity.
Further, although the above-described art using the electrostatic-type micro-actuator is an art to obtain a displacement by a voltage applied between a plurality of plate-shaped electrodes formed by the micro-machining, structurally, it is difficult to raise a resonant frequency, and as the result, a problem is immanent that vibrations are hardly attenuated when operated at a high speed. Furthermore, in view of the principle of displacement, there is a feature that the linearity of the voltage-displacement property is inferior, and from a viewpoint of an accurate positioning, there are many problems to be solved. Furthermore, the process of micro-machining per se is problematical in the fabrication cost.
Moreover, since the piezoelectric actuator 101 disclosed in Japanese Unexamined Patent Publication No. 10-136665 has a piezoelectric operating portion (a portion where a displacement is caused by distortion of a piezoelectric film) of a monomorph structure, an axis of the main distortion of a piezoelectric body naturally becomes coaxial or parallel with an axis of the main displacement of the piezoelectric operating portion, thus there is a problem that a displacement generated at the piezoelectric generating portion per se is small, and a displacement of a movable portion is also small. Furthermore, the piezoelectric actuator 101 per se is heavy, and as described in the official gazette of Japanese Unexamined Patent Publication No. 10-136665, it is likely to be influenced by harmful vibrations for operation, for example, residual vibrations and vibrational noises, for example, when operated at a high speed, making it necessary to suppress the harmful vibrations by filling a hole with a filler. However, the use of such filler is likely to unfavorably influence upon a displacement of the movable portion. Further, since the piezoelectric actuator 101 is constituted unavoidably with a piezoelectric/electrostrictive material per se which is inferior in mechanical strength, there is also a problem that the actuator is likely to be subjected to limitation of a shape and a use application due to the strength of the material.
The present invention is made in view of the problems of a piezoelectric/electrostrictive device described above, and it is the object of the present invention is to produce a piezoelectric/electrostrictive device which is made capable of performing precise operation at a high speed with a low power, and is roughly classified into three categories as described hereinafter. It should be noted that xe2x80x9cpiezoelectricxe2x80x9d of a piezoelectric element, a piezoelectric film, and piezoelectric ceramics used in the present invention includes meanings of both xe2x80x9cpiezoelectricxe2x80x9d and xe2x80x9celectrostrictivexe2x80x9d.
According to the present invention, provided as a first piezoelectric/electrostrictive device is characterized in that a connecting plate, a diaphragm, and a substrate are mutually joined together such that a joining direction of the connecting plate with the substrate and a joining direction of the connecting plate with the diaphragm are mutually intersected to form a cross, and the diaphragm is straddled between the connecting plate and the substrate, a piezoelectric element is arranged on at least a part of at least one surface of the diaphragm, and the diaphragm is convexly curved in a direction perpendicular to two directions by which said cross is formed.
In this first piezoelectric/electrostrictive device, a fixing plate is also preferably joined with an end of the connecting plate. Other devices, parts, or the like of a magnetic head or the like may also be preferably fixed to a tip or the like of the connecting plate. Further, a larger displacement is also made obtainable by a structure wherein a connecting plate and a fixing plate are alternately joined to be a meandering shape, and a diaphragm with a piezoelectric element arranged thereon is straddled between neighboring connecting plates.
As to displacement modes of the first piezoelectric/electrostrictive device, there is at least any one of the displacement modes including, the xcex8 displacement mode wherein a connecting plate is swingably displaced in a joining direction of the connecting plate with a diaphragm, when a joining surface of the connecting plate with a substrate is made as a fixed plane, and the central axis perpendicularly penetrating through the center of the fixed plane is made as the reference, the xcfx86 displacement mode wherein a displacement component in a direction perpendicular to both directions of a joining direction of the connecting plate with the diaphragm and an extending direction of the central axis is added to the xcex8 displacement mode as away from the central axis, the xcexd displacement mode wherein the connecting plate is uniaxially displaced in a joining direction of the connecting plate with the diaphragm, or the xcexdz displacement mode wherein a displacement component in a direction perpendicular to both directions of a joining direction of the connecting plate with the diaphragm and an extending direction of the central axis is added to the xcex8 displacement mode as away from the central axis. It should be noted that although these displacement modes mainly comprise components in the previously described directions, components in other displacement directions are not totally excluded.
Now, according to the present invention, a second piezoelectric/electrostrictive device is provided characterized in that a fixing plate, a connecting plate, and a diaphragm are mutually joined such that a direction where the connecting plate interposes the fixing plate and a direction where the diaphragm interposes the connecting plate are mutually intersected to form a cross, the connecting plate is joined with bottom surfaces of opposite recess portions formed on a substrate, the diaphragm is joined with sides of the recess portions, a piezoelectric element is arranged on at least a part of at least one surface of the at least one diaphragm, and the diaphragm with the piezoelectric element arranged thereon is convexly curved in a direction perpendicular to two directions forming the cross.
In the second piezoelectric/electrostrictive device, the width of a connecting plate in a direction in which the connecting plate is interposed by the diaphragm may also preferably be respectively different, and the diaphragm may also be arranged so as to be joined also with a fixing plate. As a displacement mode, preferably used is either the uniaxial displacement mode, which is a planar directional displacement of the fixing plate, wherein the fixing plate is uniaxially displaced in a direction parallel to a direction in which the connecting plate is interposed by the diaphragm, or the rotational displacement mode wherein the fixing plate is rotated about the substantially central portion of the fixing plate.
In the above described first and the second piezoelectric/electrostrictive devices, it is also preferable to arrange one or more slits and/or holes, and/or to form a thin portion and a thick portion in said connecting plate. In this case a planar displacement is made efficiently obtainable.
Next, a third piezoelectric/electrostrictive device is provided characterized in that a connecting plate is straddled between bottom surfaces of opposite recess portions formed on a substrate, in the respective recess portions, at least one diaphragm is straddled between the connecting plate and side of the recess portion, a fixing plate is joined with a connecting plate so that the longitudinal direction of the fixing plate is to be in parallel with a straddling direction of the diaphragm, and a piezoelectric element is arranged on at least a part of at least one surface of the at least two diaphragms, and the diaphragm is convexly curved in a direction perpendicular to both directions of the straddling direction of the diaphragm and the straddling direction of the connecting plate.
Also, in the third device, it is preferable to make a piezoelectric/electrostrictive device in a configuration characterized in that a connecting plate, one end thereof in longitudinal direction is interposed by at least two diaphragms, and the other end thereof is interposed by at least other two diaphragms is straddled between bottom surfaces of opposite recess portions formed on the substrate, the diaphragm is joined with sides of the recess portions, a fixing plate is joined with the connecting plate such that a longitudinal direction of the fixing plate is made to be in parallel with a direction in which the connecting plate is interposed by the diaphragm, and a piezoelectric element is arranged on at least a part of at least one surface of at least two diaphragms, and the diaphragm is convexly curved in a direction perpendicular to both directions of a direction in which the connecting plate is interposed by the diaphragm and the straddling direction of the connecting plate.
In the third piezoelectric/electrostrictive device, a notch is preferably formed at a joint of a fixing plate with a connecting plate. Further, a fixing plate may be joined so as to be intersected with a connecting plate. Further, it is also preferable to have a structure that a connecting plate is split into at least two in the longitudinal direction of a fixing plate, and at least two connecting plates which are formed by splitting are joined with the fixing plate. In the above-described case where a notch is provided, if a hinge is provided on a fixing plate from the joint of the fixing plate with the connecting plate along a longitudinal direction of the fixing portion, a displacement can be enlarged, which is preferable.
In the third piezoelectric/electrostrictive device, preferably employed is a method wherein one set of piezoelectric elements which are positioned in diagonal positions are driven in the same phase about the joint of the fixing plate with the connecting plate as the center, and the other set of piezoelectric elements are driven in an opposite phase, or one set of piezoelectric elements and the other set of piezoelectric elements are driven in the same phase with a shifted time. On the other hand, one set of piezoelectric elements which are positioned in axial symmetry about an axis in the longitudinal direction of the fixing plate as the axis of symmetry are driven in the same phase and the other set of piezoelectric elements in the opposite phase, or one set of piezoelectric elements are driven in an opposite phase, or the other set of piezoelectric elements may be driven in the same phase with a shifted time. Meanwhile, a pair of diaphragms which interposes said connecting plate may be respectively joined with a connecting plate at a position shifted in the thickness direction of the connecting plate, and it is also preferable that a piezoelectric element is arranged on a planar surface of one of respective diaphragms about the middle point of a joint of two diaphragms interposing a connecting plate with a connecting plate as the center of the point symmetry, and the piezoelectric element is driven in the same phase.
As a displacement mode of the third piezoelectric/electrostrictive device preferably employed is at least any of the displacement modes of the uniaxial displacement mode in which displacement is performed uniaxially in the longitudinal direction of the fixing plate, the in-plane rotational displacement mode having vicinity of the joint of a fixing portion with a connecting plate as the center of rotation, or the axially rotational displacement mode having an axis in the longitudinal direction of the connecting plate as the rotational center. The in-plane rotational displacement mode of the third piezoelectric/electrostrictive device is characterized in that it is based on an enlargement mechanism which enlarges a displacement of a piezoelectric device in two stages.
In the piezoelectric/electrostrictive device described above of the present invention, it is also preferable to have a structure in which one fixing plate is joined with a connecting plate in number of piezoelectric/electrostrictive devices. Further, as a convex shape of a diaphragm, when the length of a diaphragm in the straddling direction is set L, and to be the height of a curvature in the convex direction is set to be H, it is preferable if a relation at least of 1xe2x89xa6(H/L)xc3x97100xe2x89xa630 is satisfied, and it is more preferable if a relation of 1xe2x89xa6(H/L)xc3x97100xe2x89xa610 is satisfied. Further, it is preferable that at least a connecting plate and a diaphragm are joined together on the mutual sides. Namely, it is preferable if a connecting plate is displaced in the rigid body mode. If at least a connecting plate, a diaphragm, and a substrate are integrally formed, it is preferable as the reliability of the joint is raised. Of course, when a fixing plate is arranged, it is also preferable that the fixing plate is joined at the side thereof in the similar way, and it is integrally formed with the connecting plate. Such integrated structure can easily be obtained by forming at least the connecting plate, the diaphragm, and the substrate, by use of the green sheet laminating method. In this case, a fixing plate can easily be integrally formed in a similar way.
One piezoelectric element may be split into a plurality thereof, and in this case, it is preferable that at least one split piezoelectric element is used as a driving element, and at least one other piezoelectric element is used as an auxiliary element. Further, irrespective of whether one piezoelectric element is split or not, when two or more piezoelectric elements are arranged, it is also preferable that at least one piezoelectric element is used as a driving element, and at least one other piezoelectric element is used as an auxiliary element. Further, it should be noted that an auxiliary element here means a trouble diagnosing element, a displacement confirming and judging element, a driving assisting element, or the like.
An electrode lead for causing a current to flow to a piezoelectric element or an electrode of the piezoelectric element is, when coated by an insulating layer composed of a resin or glass, preferably improves the humidity resistance. If a resin is used here, a resin fluorite or a silicone resin may be preferably used. When an insulating layer is formed, it is preferable to form a shielding layer composed of a conductive material on the surface thereof.
As a material of a substrate, a fixing plate, a connecting plate, and a diaphragm, fully-stabilized zirconia or partially-stabilized zirconia is preferably used. On the other hand, for a piezoelectric film at a piezoelectric element, a material containing lead zirconate, lead titanate, or lead magnesium niobate as the major component is preferably used. A shape of at least any of the fixing plate, the connecting plate, and the diaphragm can be easily adjusted of the dimensions thereof by trimming by use of the laser machining or the mechanical machining, and it is also preferable to adjust the available electrode area of the piezoelectric element by machining the electrode in the piezoelectric element by use of the laser machining or the mechanical machining.
By the way, if a piezoelectric/electrostrictive device according to the present invention is compared with the piezoelectric actuator 101 described above in the official gazette of Japanese Unexamined Patent Publication No. 10-136665, the piezoelectric/electrostrictive device according to the present invention has a unimorph- or bimorph-type structure having a diaphragm, and thus has a feature that the axis for main distortion of a piezoelectric film and the axis for main displacement of a piezoelectric operating portion have mutually different directions, and a distortion of the piezoelectric film can be enlarged using this feature, and thus a large displacement of the fixing plate can be obtained. Further, the piezoelectric/electrostrictive device of the present invention can have functions thereof divided, and as a substrate and the like except a piezoelectric film can be composed of a material containing zirconia, which is superior in the mechanical strength and the rigidity, as the major component thereof, there is an advantage that a device, having desired strength, and compactified, thinner in thickness, and lighter in weight, can be obtained. Further, there is a feature that the device can be scarcely influenced from the outside to the displacement property, and therefore a filler or the like is unrequited.